1. Field of the Disclosure
The present invention relates to a semiconductor light emitting diode, and more particularly, to a semiconductor light emitting diode having a textured structure to improve the light extraction efficiency and a method of manufacturing the same.
2. Description of the Related Art
A light emitting diode (LED) is a device used for converting electrical energy into infra red rays, visible light, or other light using the characteristics of a compound semiconductor. The light emitting diode is a kind of electro luminescent (EL) device, and at the present time the light emitting diodes that employ an III-V group compound semiconductor are being practically used.
The III-V group compound semiconductor is a direct transition type semiconductor, and is widely used for LEDs or laser diodes (LDs) since it provides stable operation at a higher temperature than devices that use other semiconductors. The III-V group compound semiconductor is typically formed on a substrate formed of sapphire Al2O3 or SiC. To improve light emission efficiency, or light extraction efficiency, LEDs having a variety of structures have been studied. Current studies utilize a textured structure on a light extraction region of the LED to improve the light extraction efficiency.
At an interface between material layers having different refractive indexes, the passing of light is interrupted by different refractive indexes of the material layers. In the instance of a flat interface, when light passes from a semiconductor layer having a greater refractive index (n=2.5) into an air layer having a smaller refractive index (n=1), the light must enter the flat interface at less than a predetermined angle with respect to the normal to the flat surface. If the light enters at an angle greater than the predetermined angle, the light internally reflects in its totality at the flat interface, thereby greatly reducing the light extraction efficiency. To avoid the total internal reflection of light, a method of incorporating a textured structure at the interface has been attempted.
FIGS. 1A and 1B are cross-sectional views illustrating a conventional light emitting diode having a textured structure. Referring to FIG. 1A, a p-GaN layer 102, an active layer 103, an n-GaN layer 104 are sequentially formed on a p-electrode 101, and an n-electrode 105 is formed on the n-GaN layer 104. When light generated by the active layer 103 is extracted upward through the n-GaN layer 104, a textured structure 106 is incorporated at an interface between the n-GaN layer 104 and the air layer to change the incidence angle of the light.
Referring to FIG. 1B, an n-GaN layer 112 is formed on a sapphire substrate 111, and an n-AlGaN layer 113, an active layer 114, a p-AlGaN layer 115, a p-GaN layer 116, and a p-electrode 117 are sequentially formed on a region of the n-GaN layer 112. An n-electrode 118 is formed on a region of the n-GaN layer 112 where the n-AlGaN layer 113 is not formed. This is a flip-chip structure in which light generated by the active layer 114 is primarily extracted through the transparent sapphire substrate 111. Here, the light extraction efficiency is improved by forming a textured structure 120 on the surface of the sapphire substrate 111.
A conventional semiconductor light emitting diode incorporates the textured structure 120 to improve the light extraction efficiency. However, particularly as depicted in FIG. 1B, when the textured structure 120 is incorporated by patterning the sapphire substrate 111, the growth of a uniform semiconductor layer on the sapphire substrate 111 is difficult because the unmatched crystal structure between the sapphire substrate 111 and the semiconductor layer is likely to cause defects in the semiconductor layer, thereby reducing the light extraction efficiency.